Process for the conversion of lignocellulose material into an organic acid

ABSTRACT

The invention relates to a process for the conversion of lignocellulose into an organic acid including an alkaline pretreatment step and a fermentation step, wherein liquid phase obtained in the fermentation step is recycled to the alkaline pretreatment step and/or the fermentation step. Organic acid is recovered as its magnesium of calcium salt from solid phase obtained in the fermentation step.

FIELD OF THE INVENTION

The present invention relates to a process for the conversion oflignocellulose material into an organic acid.

BACKGROUND OF THE INVENTION

It is known to produce organic acids, such as for example lactic acid,succinic acid, or acetic acid by fermentation of biomass that compriseslignocellulose. In WO2009/025547 is for example disclosed a process forthe production of lactic acid as a fermentation product fromlignocellulosic biomass. In the process of WO2009/025547 lignocellulosicbiomass is pretreated with an alkaline agent and then subjected tosimultaneous saccharification and fermentation in a fermentor to producelactic acid or a salt thereof.

A disadvantage of the process of WO2009/025547 is that the fermentationproduct, i.e. lactic acid or calcium lactate, is recovered in arelatively low concentration. In case the lactic acid recovered would beused for subsequent microbial conversion into ethanol, multipledistillation steps would be needed in order to obtain an ethanolconcentration of 96%.

Further, a relatively low yield of the fermentation product will beobtained. In order to obtain sufficient saccharification of thelignocellulose, a relatively severe alkaline pretreatment step, aprehydrolysis step, and/or a relatively high amount of hydrolytic enzymein the fermentor would be needed.

SUMMARY OF THE INVENTION

It has now been found that if the production of organic acid fromlignocellulose material by alkaline pretreatment followed byfermentation of the alkaline pretreated material in a fermentation zoneis carried out such that liquid effluent of the fermentation zone isrecycled to the alkaline pretreatment step and/or to the fermentationzone, and the organic acid is recovered as magnesium or calcium saltfrom the solid effluent of the fermentation zone, the organic acid canbe obtained in a high concentration, with a high yield and at a highpurity.

Accordingly, the invention relates to a process for the conversion oflignocellulose into an organic acid, the process comprising thefollowing steps:

-   -   a) pretreating a feed comprising lignocellulose material with an        alkaline agent comprising a divalent cation, wherein the        divalent cation is a calcium or magnesium cation, in the        presence of water at a pretreatment temperature, to obtain an        aqueous slurry of alkaline pretreated lignocellulose material;    -   b) supplying at least part of the slurry of alkaline pretreated        lignocellulose material to a fermentation zone and subjecting        the pretreated lignocellulose material, in the fermentation zone        in the presence of a hydrolytic enzyme and a micro-organism that        is able to convert saccharides into an organic acid, to        enzymatic hydrolysis and fermentation to obtain a fermentation        broth comprising insoluble lignocellulose, precipitated and        dissolved salt of the organic acid with the divalent cation, and        enzyme;    -   c) discharging fermentation broth obtained in step (b) from the        fermentation zone;    -   d) separating from the fermentation broth a liquid phase        comprising the dissolved salt of the organic acid and a solid        phase comprising insoluble lignocellulose and the precipitated        salt of the organic acid; and    -   e) recycling at least part of the liquid phase to alkaline        pre-treatment step a) and/or to the fermentation zone.

Since liquid phase is recycled over the fermentation zone, i.e.indirectly via recycling to the alkaline pretreatment step and/ordirectly, a high conversion per pass of fermentable saccharides intoorganic acid is not needed in order to obtain a high yield. Unconvertedfermentable saccharides will be recycled and can be fermented in a nextpass. Therefore, also saccharides that are relatively difficult toferment, such as for example cellulose oligomers and xylose, can befermented without the need of a large fermentation zone.

Since part of the hydrolytic enzyme will be recycled with the liquidphase, a relatively low amount of enzyme can be used.

An important advantage of the process according to the invention is thatthe product, i.e. the organic acid or the calcium or magnesium saltthereof, can be obtained in a relatively high concentration. Due to therecycle, the concentration of dissolved calcium or magnesium salt of theorganic acid will accumulate until saturation is achieved. Oncesaturation is achieved, any further organic acid produced in thefermentation zone will precipitate as its calcium or magnesium salt.Thus, also under process conditions wherein a relatively low amount oforganic acid is produced per pass, for example because of a lowconcentration of lignocellulose and/or of hydrolytic enzyme and/orbecause of a poor hydrolysis of the lignocellulose material, the productcan still be obtained in a desired high yield and concentration. Anadvantage of producing for example lactic acid in a relatively highconcentration is that, if the lactic acid is further converted intoother chemicals, e.g. by fermenting the lactic acid into succinic acidor ethanol, such chemicals can also be obtained in a relatively highconcentration. In case of the fermentation of lactic acid into ethanol,this implies that less distillation steps are needed to obtainconcentrated ethanol.

Also soluble products of the process according to the invention, such asfor example amino acids or peptides in case of a protein-containingfeed, can be recovered in a sufficiently high concentration since suchamino acids or peptides will accumulate in the liquid effluent of thefermentation zone due to the recycle.

A further advantage of the process according to the invention is that itis economically viable to carry it out on a small scale. The process canbe operated at atmospheric pressure and is therefore much less capitalintensive than known processes for conversion of lignocellulosematerial. If carried out on a small scale, i.e. by using waste biomassoriginating from a relatively small area of farm land as lignocellulosematerial, waste streams from the process according to the invention,such as minerals, lignocellulose residue or calcium carbonate, can bespread out over the farm land from which the lignocellulose materialoriginated in order to increase soil fertility. Thus, transportationcosts and costs for concentration of waste streams are avoided.

SUMMARY OF THE DRAWING

In the FIGURE an embodiment of the invention is schematically shown.

DETAILED DESCRIPTION OF THE INVENTION

In the process according to the invention, a feed comprisinglignocellulose material is first subjected to an alkaline pretreatment(step a)) and then supplied to a fermentation zone wherein it issubjected to enzymatic hydrolysis and fermentation (step b)). In thefermentation zone, polysaccharides in the lignocellulose material arehydrolysed to obtain fermentable saccharides, which are fermented intoone or more organic acids. A fermentation broth is obtained that isdischarged from the fermentation zone (step c)) and then separated intoa liquid phase and a solid phase (step d)). At least part of the liquidphase is recycled to the alkaline pretreatment step and/or to thefermentation zone (step e)).

The lignocellulose material may be any biomass material comprisinglignocellulose. Examples of suitable lignocellulose material are wood,straw, paper, bagasse, grass, or combinations thereof. Preferably, thelignocellulose material is an agricultural waste material such as forexample straw or waste paper. The lignocellulose material may be freshmaterial or dried material. The feed may comprise lignocellulosematerial that has undergone a pretreatment such as pre-hydrolysis or anextraction step to remove non-fermentable components or to removecomponents that could inhibit the subsequent hydrolysis and fermentationin step b).

The lignocellulose material is preferably comminuted material, forexample comminuted by cutting, milling, mechanical refining or extrusionin order to improve the accessibility of the material for the alkalinepretreatment and the hydrolysis/fermentation step.

The feed may comprise material other than lignocellulose material, suchas domestic waste or industrial residues (e.g. rapeseed press cake,vegetable residue or greenhouse residue). Preferably, the feed comprisesat least 30 wt % dry lignocellulose based on the dry weight of organicmaterial in the feed, more preferably at least 50 wt %, even morepreferably at least 70 wt %.

In step a), the lignocellulose material is pretreated in order to breakopen the lignocellulose matrix, to remove lignin, to make lignin moreaccessible and/or to increase the surface area of the cellulose. As aresult of the pretreatment, the lignocellulose material will be moresuitable for subsequent hydrolysis and fermentation in step b). Alkalinepretreatment of lignocellulose material is well-known in the art. Anysuitable alkaline pretreatment conditions known in the art may beapplied in step a).

The feed is pretreated with an alkaline agent comprising a divalentcation, wherein the divalent cation is calcium or magnesium, in thepresence of water. The alkaline agent may for example be calciumhydroxide, calcium oxide, magnesium hydroxide, magnesium oxide, or acombination of two or more thereof. Preferably the alkaline agent iscalcium hydroxide or calcium oxide, more preferably calcium hydroxide.Typically, the amount of water present is such that the concentration ofdry solid lignocellulose is in the range of from 5 to 30 wt % based onthe volume of aqueous phase. The amount of alkaline agent is preferablysuch that a slurry is obtained with a pH in the range of from 8.0 to14.0, more preferably of from 8.5 to 13.0, even more preferably of from9.0 to 12.0.

The alkaline pretreatment may be carried out at any suitablepretreatment temperature. Preferably, the pretreatment temperature is inthe range of from 20 to 115° C., more preferably of from 50 to 100° C.,even more preferably of from 60 to 98° C., still more preferably of from70 to 95° C.

It will be appreciated that, since the severity of the alkalinepretreatment is not critical in the process according to the invention,the time during which the lignocellulose material is pretreated is notcritical either. The material may be pretreated during any suitable timeperiod, for example during a time in the range of from 10 minutes to 100days, preferably of from 20 minutes to 3 hours, more preferably of from30 to 60 minutes. It will be appreciated that typically, a lowerpretreatment temperature will be combined with a longer pretreatmenttime.

In step a), an aqueous slurry of alkaline pretreated lignocellulosematerial is obtained. At least part of the slurry is supplied to afermentation zone. Preferably, at least 70%, more preferably at least 80of the slurry will be supplied to the fermentation. Large particles orfibres, preferably particles or fibres with a diameter (particles) orlength (fibres) of at least 2 mm are separated from the slurry prior tosupplying the slurry to the fermentation zone. Alternatively, forexample in case a feed comprising a mixture of different lignocellulosematerials with different cellulose contents is used, part of thepretreated lignocellulose material may be separated from the slurry foruse in a different process, and the remainder of the slurry will besupplied to the fermentation zone. It may for example be advantageous toseparate a pretreated lignocellulose material with a relatively highcellulose content from the slurry in order to use it for papermanufacturing.

The slurry may be subjected to a cooling step or a screening step (forremoving large particles or fibres) prior to be supplied to thefermentation zone. In case the pretreatment temperature is higher thanthe temperature at which the hydrolysis and fermentation are carriedout, the alkaline pretreated material is preferably first cooled to thehydrolysis/fermentation temperature.

The slurry comprising pretreated lignocellulose material is supplied toa fermentation zone comprising one or more fermentors in series. Theslurry may be batch-wise or continuously supplied to the first fermentorin the fermentation zone.

In the fermentation zone, the pretreated material is subjected, in thepresence of a hydrolytic enzyme and a micro-organism that is able toconvert saccharides into an organic acid, to enzymatic hydrolysis andfermentation. The hydrolytic enzyme may be any enzyme suitable for thehydrolysis of saccharides in lignocellulose material or combinations ofone or more of such enzymes. Such enzymes are known in the art andinclude cellulase, hemicellulase or combinations thereof, optionally incombination with pectinase or cellobiase. Preferably, at least acellulase is present as enzyme.

The micro-organism may be any micro-organism or a combination ofmicro-organisms suitable for converting saccharides into one or moreorganic acids. Such micro-organisms are known in the art and includebacteria and fungi such as yeast. Preferably, the micro-organism is alactic acid producing micro-organism, more preferably a lactic acidproducing bacterium. Examples of suitable lactic acid producing bacteriaare lactobacilli, bifidobacteria, certain Bacillus and Streptococcusspecies or combinations thereof.

The temperature in the one or more fermentors may be any temperature atwhich enzymatic hydrolysis and fermentation takes place. Preferably, thetemperature is in the range of from 20 to 80° C., more preferably offrom 25 to 60° C., even more preferably in the range of from 30 to 50°C. In case the fermentation zone comprises more than one fermentors, thetemperature may be different in the different fermentors.

The fermentation may be carried out at any suitable pH, preferably at apH in the range of from 4.0 to 8.0, more preferably of from 4.5 to 7.5.a pH in the range of from 5.0 to 7.0 is particularly preferred. It willbe appreciated that in case the fermentation zone comprises more thanone fermentors in series, the pH in a subsequent fermentor willtypically be lower than in a preceding fermentor due to additionalorganic acid formed.

Under the conditions prevailing in the one or more fermentors in thefermentation zone, polysaccharides in the lignocellulose material arefirst hydrolysed to obtain fermentable saccharides that may includemonosaccharides such as glucose, mannose, fructose, mannose, rhamnose,xylose, arabinose, galacturonic acid, disaccharides such as lactose,xylobiose and cellobiose and oligomeric saccharides. The fermentablesaccharides are fermented into one or more organic acids by themicro-organism(s) present. It will be appreciated that it will mainlydepend on the micro-organism present which organic acid is formed. Theorganic acid formed as fermentation product may be lactic acid, citricacid, itaconic acid, succinic acid, fumaric acid, glycolic acid, pyruvicacid, acetic acid, glutamic acid, malic acid, propionic acid, butyricacid, gluconic acid and combinations thereof. Preferably, themicro-organism is a lactic acid producing micro-organism, morepreferably a lactic acid producing bacterium, and the organic acidformed is lactic acid.

Thus, in the one or more fermentors, a fermentation broth is obtainedthat comprises insoluble lignocellulose, an organic acid, dissolved saltof the organic acid and the divalent cation, the enzyme, themicro-organism and, once the concentration of dissolved salt of theorganic acid has achieved saturation, precipitated salt of the organicacid and the divalent cation. The fermentation broth may comprisenon-fermented saccharides.

In case of more than one fermentors in series, typically the entirefermentation broth formed in a fermentor is supplied to the nextfermentor in series.

Fermentation broth is discharged from the fermentation zone. In case thefermentation zone comprises more than one fermentors in series,fermentation broth is discharged from the last fermentor in series. Thefermentation broth discharged is separated into a liquid phase and asolid phase. Such separation may be done by any suitable means known inthe art, such as centrifugation, filtration or sedimentation.

At least part of the liquid phase is recycled to the alkalinepretreatment step and/or to the fermentation zone. Preferably at least50 vol %, more preferably at least 80 vol %, even more preferably atleast 90 vol % and still more preferably at least 95 vol % of the liquidphase is recycled to the alkaline pretreatment step and/or to thefermentation zone. Preferably a small part of the liquid phase,preferably at most 10 vol %, more preferably at most 5 vol % of theliquid phase is removed from the process as a bleed stream.

Preferably, at least part of the liquid phase, more preferably at least50 vol %, even more preferably at least 80 vol %, is recycled topretreatment step a). Thus, use is made of the water present in theliquid phase and too much dilution of the dissolved salt of the organicacid in the liquid phase is therewith avoided. It may be advantageous torecycle at least part of the liquid phase directly to the fermentationzone to avoid inactivation of the enzyme that may be present in therecycled liquid phase. In order to strike a balance between undesireddilution and enzyme inactivation, preferably part of the liquid phase isrecycled to pretreatment step a) and part directly to the fermentationzone. Preferably at most 50 vol %, more preferably at most 20 vol % ofthe liquid phase is directly recycled to the fermentation zone.

In case the fermentation zone comprises more than one fermentors, partof the liquid phase may be recycled over a single fermentor or to apreceding fermentor.

The liquid phase comprises dissolved salt of the organic acid and thedivalent cation. The liquid phase may further comprise the organic acid,dissolved fermentable saccharides, enzyme, micro-organism and othersoluble or solubilised compounds from the lignocellulose material. As aresult of the recycle, the dissolved salt of the organic acid willaccumulate in the liquid phase until its saturation concentration isreached. Any additional organic acid produced in the fermentation zonewill then result in precipitation of the organic acid produced in theform of its calcium or magnesium salt. Thus, after a certain time onstream, a fermentation broth will be obtained that comprisesprecipitated salt of organic acid. The precipitated salt will bedischarged from the fermentation zone with the broth and end up, afterseparation, in the solid phase. The salt of the organic acid can berecovered from the solid phase by means known in the art, for example bymeans of solid-liquid extraction.

Because the liquid phase is recycled, it is not necessary to achieve ahigh conversion of saccharides into organic acid per pass. Once theconcentration of dissolved salt of the organic acid has reached itssaturation concentration, any organic acid further formed willprecipitate as its divalent cation salt. The salt can be recovered fromthe solid phase in a relatively high concentration. Therefore,parameters that influence the rate of conversion for the hydrolysis andthe fermentation in the fermentation zone such as the severity of thealkaline pretreatment, the amount of enzyme or micro-organism, pH andtemperature in the fermentor(s), residence time in the fermentor(s), thefermentability of the saccharides and the concentration of alkalinepretreated lignocellulose material, are less critical. The operatingwindow is therefore much wider than in prior art processes forhydrolysis and fermentation of lignocellulose material, such as forexample the process as disclosed in WO2009/025547.

Preferably, the fermentation comprises in the range of from one to fivefermentors in series, more preferably of from one to three fermentors inseries.

In case the fermentation zone comprises more than one fermentors inseries, it may be advantageous to apply different process conditions inthe different fermentors, for example by applying a differenttemperature, pH, residence time and/or by using different hydrolyticenzymes. It may for example be advantageous to operate the firstfermentor at a temperature higher than the optimum temperature of themicro-organism, preferably at a relatively short residence time, and tooperate succeeding fermentors at a lower temperature in order to operatecloser to the optimum temperature of the micro-organism and/or toenhance precipitation of the salt of the organic acid.

The solid phase that is separated from the fermentation broth that isdischarged from the fermentation zone may be washed in order to removecontaminants such as fermentation inhibitors and/or any dissolvedcalcium or magnesium salt of the organic acid and fermentablesaccharides from the solid phase. Such washing is carried out at a lowtemperature in order to avoid too much dissolution of the precipitatedsalt of the organic acid. Preferably, the washing is carried out at atemperature in the range of from 10 to 50° C., more preferably of from15 to 40° C. Washing at room temperature is particularly preferred.Washed solid phase and wash water is thus obtained. At least part of thewash water can advantageously be recycled to step a) to provide thewater in pretreatment step a), or to the fermentation zone. Recycling tostep a) is particularly preferred since any fermentation inhibitorspresent in the wash water will typically be decomposed intonon-inhibiting compounds under the conditions prevailing in step a).

The calcium or magnesium salt of the organic acid may be recovered fromthe solid phase that is separated from the fermentation broth,preferably after washing. Such recovery may for example be carried outby extraction of the solid phase with water at elevated temperature,preferably at a temperature in the range of from 50 to 120° C., morepreferably of from 60 to 100° C. Thus, a concentrated solution of thecalcium or magnesium salt of the organic acid in water and an extractedsolid phase are obtained. The solution may comprise up to 40 wt % saltof the organic acid. The concentrated solution of the salt may berecovered as product. Alternatively, the salt may be recovered as solidproduct by cooling the solution in order to precipitate the salt andthen recovering the precipitated salt as solid product.

The calcium or magnesium salt of the organic acid thus obtained may forexample be used as ingredient for a feed composition or as raw materialfor fermentation processes such as fermentation of the organic acid intoethanol or succinic acid.

It is an advantage of the process according to the present inventionthat the salt of the organic acid can be obtained in a highlyconcentrated form and in a relatively pure form. In case the organicacid is lactic acid, relatively low amounts of acetic acid, furfural andother compounds that may act as an inhibitor for the furtherfermentation of the lactic acid into products like ethanol of succinicacid, are present. In the process according to the invention, suchcompounds dissolve in the liquid phase and are recycled to the alkalinepretreatment step a) and/or the fermentation zone or are removed fromthe process with a bleed stream from the liquid phase. In the alkalinepretreatment step, such compounds will typically be decomposed intocompounds that do not act as fermentation inhibitors.

In an embodiment of the invention, the feed comprises protein. The feedmay for example comprise protein if it contains a protein-containinglignocellulose material. Examples of suitable protein-containinglignocellulose material are agricultural residues such as sugar beetleaves, beet pulp, potato fibres, potato leaves and peels and press cakefrom oilseed processing, rape seed straw, vegetable agriculturalresidues, dried distiller's grains with solubles (DDGS), wet distiller'sgrain or other highly diluted residues from food or biofuel processes,rape meal or sunflower meal from which most protein is extracted. Suchprotein-containing lignocellulose material may constitute the entirefeed, but may also be part of the feed, the feed further comprisinganother lignocellulose material. An advantage of using a feed thatcomprises protein is that the adsorption of enzyme, in particular theadsorption of cellulase and beta-glucosidase, on the lignin present inthe lignocellulose material will be reduced during fermentation step b).Thus, enzyme costs will be reduced compared to a process using a feedwithout protein.

Further, in case the feed comprises protein, amino acids and/or peptidesmay be advantageously recovered as product from the liquid phase. Incase the feed stream comprises protein and recovery of amino acids orpeptides is desired, the micro-organism is preferably a micro-organismthat is able to hydrolyse protein into its amino acids or peptides. Morepreferably, the micro-organism is a lactic-acid producing bacterium.Amino acids and/or peptides formed in the fermentation zone may berecovered from the liquid phase by means known in the art, for exampleby evaporation of the liquid phase.

Preferably, the process further comprises a fermentation step whereinthe organic acid in the salt of the organic acid that is recovered fromthe solid phase is fermented into a fermentation product. In case theorganic acid is lactic acid, the calcium or magnesium lactate recoveredfrom the solid phase may for example be fermented into succinic acid orethanol. The fermentation product is then recovered as product by meansknown in the art. Recovery of ethanol from such fermentation istypically done by means of distillation.

It may be advantageous to add a further acid, i.e. an acid that can bedistinguished from the organic acid, during such fermentation step inorder to minimize the pH increase due to the conversion of the organicacid. If such further acid is added, a calcium or magnesium salt of thefurther acid is formed as co-product of the fermentation step. Examplesof suitable further acids are sulphuric acid, hydrochloric acid,phosphoric acid.

The extracted solid phase can suitably be used as feed to a powergenerator. Since the extracted solid phase typically has a low potassiumcontent, slag formation in the power generator is avoided. Mostpotassium present in the lignocellulose material will typically bedischarged from the process with a bleed stream from the liquid phase.Preferably, the extracted solid phase is fed to the power generator asco-feed together with a feed such as for example natural gas, biomass orwaste paper. In the power generator, electricity and heat are generated.Preferably, the heat generated is used in step a) to achieve the desiredpretreatment temperature.

In an embodiment of the invention, the feed to alkaline pretreatmentstep a) comprises paper comprising calcium carbonate. In case papercomprising calcium carbonate is used as feed, the extracted solid phasewill comprise calcium carbonate. In case such extracted solid phasecomprising calcium carbonate is fed to the power generator, calciumoxide will be formed in the power generator. Preferably, such calciumoxide is recycled to alkaline pretreatment step a) as alkaline agent.

As described in more detail hereinabove, in some embodiments of theinvention, a magnesium or calcium salt of the further acid is formed inthe fermentation of the (salt of the) organic acid recovered from thesolid phase. The magnesium or calcium salt of the further acid thusformed may be co-fed to the power generator to form magnesium or calciumoxide. Preferably, such magnesium or calcium oxide is recycled toalkaline pretreatment step a) as alkaline agent.

Alkaline pretreatment step a) is carried out in the presence of water.External water may be directly added to alkaline pretreatment step a).Alternatively, water used in extraction of washing steps in the processaccording the invention may be recycled to step a). Examples of suchwater is water that is used to dissolve calcium or magnesium salt of theorganic acid from the solid phase obtained in step d), water that isused to wash the extracted solid phase before it is fed to the powergenerator, or water that is used to wash a high cellulose alkalinepretreated lignocellulose material that is separated from the slurryobtained in step a). Instead of water, aqueous streams that compriseorganic material may be used to provide the water in step a), such asfor example wet distiller's grain or other streams from food or biofuelprocesses.

DETAILED DESCRIPTION OF THE DRAWING

In the FIGURE, an embodiment of the invention is schematically shown.Streams of air dry, ground wheat straw 1, calcium hydroxide 2 and water3 are supplied to container 4 and kept in the container at apretreatment temperature of 95° C. during 24 hours. After 24 hours, anaqueous slurry of alkaline pretreated straw 5 is discharged fromcontainer 4 and supplied to fermentation zone 6 that comprises a singlefermentor. Cellulase enzymes, a lactic-acid producing bacterium andnutrients are added to fermentor 6 (not shown). In fermentor 6, thealkaline pretreated lignocellulose material is subjected to enzymatichydrolysis to form fermentable saccharides. The saccharides thus formedare fermented into lactic acid. Due to the presence of calcium ions infermentor 6, the lactic acid formed will dissolve as calcium lactate andafter the saturation concentration has been reached, calcium lactateprecipitates. Fermentation broth 7 comprising insoluble lignocellulose,dissolved and precipitated calcium lactate, and cellulase is dischargedfrom fermentation zone 6 and supplied to separator 8 wherein it isseparated into liquid phase 9 and solid phase 10. A small stream 11 ofliquid phase is removed from the process as bleed stream. The main part12 of liquid phase is recycled to container 4, i.e. to the alkalinepretreatment step. Liquid phase 9 comprises dissolved calcium lactate,lactic acid and optionally part of the cellulase and some fermentablesaccharides. Solid phase 10 comprises insoluble lignocellulose andprecipitated calcium lactate. The solid phase is supplied tosolid-liquid extraction unit 13 wherein the solid phase iscounter-currently extracted with hot water to obtain extracted solidphase 14 and an aqueous solution of calcium lactate 15. Solution 15 maybe recovered as product. Alternatively, solution 15 is cooled (notshown) to precipitate the calcium lactate and solid calcium lactate isrecovered as product. Instead of recovering calcium lactate as product,the calcium lactate may be further fermented into ethanol or otherfermentation products (not shown).

Extracted solid phase 14 is supplied as co-feed to power generator 16,together with main feed 17 that may for example be natural gas, biomassand/or waste paper. In generator 16, electricity 18 and heat 19 aregenerated. Heat 19 is used to heat the content of container 4 to thepretreatment temperature of 95° C.

1. A process for the conversion of lignocellulose into an organic acid, the process comprising the following steps: a) pretreating a feed comprising lignocellulose material with an alkaline agent comprising a divalent cation, wherein the divalent cation is a calcium or magnesium cation, in the presence of water at a pretreatment temperature, to obtain an aqueous slurry of alkaline pretreated lignocellulose material; b) supplying at least part of the slurry of alkaline pretreated lignocellulose material to a fermentation zone and subjecting the pretreated lignocellulose material, in the fermentation zone in the presence of a hydrolytic enzyme and a micro-organism that is able to convert saccharides into an organic acid, to enzymatic hydrolysis and fermentation to obtain a fermentation broth comprising insoluble lignocellulose, precipitated and dissolved salt of the organic acid with the divalent cation, and enzyme; c) discharging fermentation broth obtained in step (b) from the fermentation zone; d) separating from the fermentation broth a liquid phase comprising the dissolved salt of the organic acid and a solid phase comprising insoluble lignocellulose and the precipitated salt of the organic acid; and e) recycling at least part of the liquid phase to alkaline pre-treatment step a) and/or to the fermentation zone.
 2. A process according to claim 1, wherein at least part of the liquid phase is recycled to step a).
 3. A process according to claim 2, wherein at least 50 vol % of the liquid phase is recycled to step a).
 4. A process according to any one of the preceding claim 1, wherein the fermentation zone comprises at least two fermentors in series and wherein in step c) fermentation broth is discharged from the last fermentor in series.
 5. A process according to claim 1, further comprising washing the solid phase obtained in step d) with water at a temperature in the range of from 10 to 50° C. to obtain washed solid phase and wash water and supplying at least part of the wash water to step a).
 6. A process according to claim 1, further comprising recovering the salt of the organic acid from the solid phase.
 7. A process according to claim 6, comprising extracting the solid phase obtained in step d), optionally after washing, with water at a temperature in the range of from 60 to 100° C. to obtain a solution of the salt of the organic acid and an extracted solid phase.
 8. A process according to claim 7 further comprising cooling the solution to obtain precipitated salt of the organic acid and recovering the precipitated salt in solid form.
 9. A process according to claim 6, further comprising a fermentation step wherein the salt of organic acid is fermented into a fermentation product and the fermentation product is recovered as product.
 10. A process according to claim 9, wherein a further acid is added during the fermentation step and a calcium or magnesium salt of the further acid is formed as co-product in the fermentation step.
 11. A process according to claim 7, further comprising feeding the extracted solid phase to a power generator to generate electricity and waste heat.
 12. A process according to claim 11, wherein the feed comprises paper comprising calcium carbonate and wherein calcium oxide is formed in the power generator and wherein calcium oxide formed in the power generator is recycled to alkaline pretreatment step a) as alkaline agent.
 13. A process according to claim 11, wherein the waste heat generated is used to achieve the pretreatment temperature in step a).
 14. A process according to claim 1, wherein the micro-organism is a lactic-acid producing micro-organism and the organic acid is lactic acid.
 15. A process according to claim 1, wherein the feed comprises protein.
 16. A process according to claim 15, wherein amino acids and/or peptides are recovered from the liquid phase separated from the fermentation broth. 